feat(gui): auto-detect games in Wine prefix and browse for exe

- detect::scan_games_in_prefix() walks drive_c/Program Files and
  Program Files (x86) up to depth 4, skipping Windows system dirs,
  the launcher's own exe, and already-configured games
- Empty game list now shows "No games added yet." with two actions:
    · Scan for games — async scan of the Wine prefix, results appear
      as a clickable list with + buttons to add each found exe
    · Browse exe… — native file picker (zenity/kdialog) opening in
      drive_c/, computes the relative path automatically
- Add-game form gains a Browse… button to pick exe from the prefix
- util::pick_file() added alongside pick_folder()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/detect.rs

@@ -1,7 +1,7 @@
-use crate::config::Config;
+use crate::config::{Config, Launcher};
 use anyhow::Result;
 use owo_colors::OwoColorize;
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::path::{Path, PathBuf};
 
 #[derive(Debug, Clone)]
@@ -36,6 +36,99 @@ pub fn scan_for_gui(config: &Config) -> Vec<DetectHit> {
     hits
 }
 
+/// Directories inside drive_c that contain Windows system files, not games.
+const SYSTEM_DIRS: &[&str] = &[
+    "windows",
+    "users",
+    "programdata",
+    "internet explorer",
+    "windows media player",
+    "windowspowershell",
+    "microsoft.net",
+    "common files",
+    "microsoft",
+    "windows nt",
+    "windowsapps",
+];
+
+/// Scan a launcher's Wine prefix for installed game executables.
+/// Returns (display_name, path_relative_to_drive_c) pairs, sorted alphabetically,
+/// excluding the launcher's own exe and any already-configured games.
+pub fn scan_games_in_prefix(launcher: &Launcher) -> Vec<(String, String)> {
+    let drive_c = launcher.prefix_dir.join("drive_c");
+    if !drive_c.exists() {
+        return vec![];
+    }
+    let search_dirs = [
+        drive_c.join("Program Files"),
+        drive_c.join("Program Files (x86)"),
+    ];
+    let already: HashSet<String> = launcher
+        .games
+        .iter()
+        .map(|g| g.exe_path.to_string_lossy().to_lowercase())
+        .collect();
+    let launcher_exe = launcher.exe_path.to_string_lossy().to_lowercase();
+
+    let mut results = Vec::new();
+    let mut seen: HashSet<String> = HashSet::new();
+    for dir in &search_dirs {
+        scan_exe_dir(dir, &drive_c, &launcher_exe, &already, &mut results, &mut seen, 0);
+    }
+    results.sort_by(|a, b| a.0.cmp(&b.0));
+    results
+}
+
+fn scan_exe_dir(
+    dir: &Path,
+    drive_c: &Path,
+    launcher_exe: &str,
+    already: &HashSet<String>,
+    out: &mut Vec<(String, String)>,
+    seen: &mut HashSet<String>,
+    depth: u32,
+) {
+    if depth > 4 {
+        return;
+    }
+    let Ok(entries) = std::fs::read_dir(dir) else { return };
+    for entry in entries.flatten() {
+        let path = entry.path();
+        let lower = path
+            .file_name()
+            .and_then(|n| n.to_str())
+            .unwrap_or("")
+            .to_lowercase();
+        if SYSTEM_DIRS.iter().any(|s| lower.starts_with(s)) {
+            continue;
+        }
+        if path.is_dir() {
+            scan_exe_dir(&path, drive_c, launcher_exe, already, out, seen, depth + 1);
+        } else if path
+            .extension()
+            .and_then(|e| e.to_str())
+            .map(|e| e.eq_ignore_ascii_case("exe"))
+            .unwrap_or(false)
+        {
+            let Ok(rel) = path.strip_prefix(drive_c) else { continue };
+            let rel_str = rel.to_string_lossy().to_string();
+            let rel_lower = rel_str.to_lowercase();
+            if rel_lower == launcher_exe || already.contains(&rel_lower) {
+                continue;
+            }
+            if !seen.insert(rel_lower) {
+                continue;
+            }
+            let display = path
+                .file_stem()
+                .and_then(|s| s.to_str())
+                .unwrap_or("Unknown")
+                .to_string();
+            out.push((display, rel_str));
+        }
+    }
+}
+
 const MAX_DEPTH: u32 = 3;
 
 pub fn run(config: &Config, extra_dirs: &[PathBuf], apply: bool) -> Result<()> {